The cave of septum pellucidum (CSP), cavum septi pellucidi, or cavity of septum pellucidum, is a slit-like space in the septum pellucidum that is present in fetuses but usually fuses during infancy. The septum pellucidum is a laminated thin translucent vertical membrane in the midline of the brain separating the anterior horns of the right and left ventricles. It lies posterior to the corpus callosum. Persistence of the cave of septum pellucidum after infancy has been loosely associated with neural maldevelopment and several mental disorders that correlate with decreased brain tissue.The cave of septum pellucidum is bounded anteriorly by the genu of the corpus callosum, superiorly by the body of the corpus callosum, posteriorly by the anterior limb and pillars of the fornix, inferiorly by the anterior commissure and the rostrum of the corpus callosum, and laterally by the leaflets of the septum pellucidum.